Historically, lubricant oil basestocks were prepared by a solvent extraction process in which a cut from a vacuum distillation unit is solvent extracted to produce a raffinate rich in paraffins and an extract rich in aromatics. The raffinate was then solvent dewaxed to address basestock quality issues such as pour point. The ability of the solvent dewaxing process to meet increased demands placed on basestock quality is limited since improvements in properties such as pour point came at the expense of basestock yield. The solvent dewaxing process is designed to separate wax from base oil thereby eliminating the highest VI components of the waxy feed. Thus in order to achieve the target pour point, high VI components are removed thereby lowering the yield.
An alternative method for preparing lubricant oil basestocks is catalytic dewaxing. Catalytic dewaxing may be accomplished by two dewaxing mechanisms: hydrocracking or hydroisomerization. The dewaxing catalysts which function by hydrocracking generally result in basestock yields which are comparable to or lower than solvent dewaxing. Dewaxing catalysts with an isomerization function can convert wax in feed to isomerate boosting yield and VI over solvent dewaxing to the same target pour point. Dewaxing catalysts which function by hydroisomerization take long chain waxy paraffins and isomerize them to branched chain species having desirable low temperature and volatility properties. Under actual operating conditions, it is not expected that a dewaxing catalyst will function exclusively by either mode of dewaxing.
Dewaxing catalysts with a hydroisomerization function are generally intolerant of heteroatom contaminants, and typically employ a hydrotreating step before dewaxing in order to remove heteroatom contaminants from the feed as such contaminants result in accelerated catalyst deactivation.
Although dewaxing catalysts with an isomerization function are well known in the art, there is still a need for catalysts which result in better yields and product qualities by minimizing hydrocracking.